Determination of phenolic compounds in medicinal preparations by galvanostatic coulometry Chimica Techno Acta LETTER published by Ural Federal University 2021, vol. 8(1), № 20218110 journal homepage: chimicatechnoacta.ru DOI: 10.15826/chimtech.2021.8.1.10 1 of 3 Determination of phenolic compounds in medicinal preparations by galvanostatic coulometry N.N. Yaschenko * , S.V. Zhitar, E.G. Zinovjeva Chuvash State University, Moskovsky Ave., 15, Cheboksary, Chuvash Republic, Russia * Corresponding author: n.yashenko.n@mail.ru This short communication (letter) belongs to the MOSM2020 Special Issue. © 2021, The Authors. This article is published in open access form under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/). Abstract In this work, the possibility of using reactions of electrogenerated ti- trants with phenolic compounds was studied and a method for their coulometric determination in medicaments by galvanostatic coulom- etry was developed. The research objects were: rutin, salicylic acid and drugs containing phenolic compounds such as «Ascorutin», «Sal- icylic Paste» and «Salicylic Ointment» of Russian manufacture. Elec- trogenerated halogens (Cl2, Br2 and I2) and hexacyanoferrate(III)- ions were used as titrants. It was found that for the quantitative de- termination of phenolic acids, the optimal reagent is electrogenerat- ed bromine, for rutin - electrogenerated bromine and iodine, and for ascorbic acid - any of the studied electrogenerated titrants (Cl2, Br2, I2 and [Fe(CN)6] 3- ). The correct definition was checked by the «en- tered-found» method, the error does not exceed 2%. As experimental studies have shown, our method of coulometric titration with elec- trogenated bromine and iodine is characterized by good reproducibil- ity of results, expression, accuracy and can be used to determine phenolic compounds in drugs, for example, «Ascorutin» tablets. It should be noted that by our procedure it is possible to determine the spectrum of phenol-containing compounds (rutin, ascorbic and sali- cylic acids) in drugs without their preliminary separation. Therefore, the coulometric method using electrogenerated titrants can be rec- ommended for the determination of salicylic, ascorbic acids and rutin in dosage forms. The proposed method is accurate and eliminates the experiment error in comparison with the Pharmacopoeic method. Keywords galvanostatic coulometry phenolic compounds flavonoids Received: 31.10.2020 Revised: 25.12.2020 Accepted: 25.12.2020 Available online: 13.04.2021 1. Introduction The phenolic group is found in the structure of many me- dicinal substances and largely determines their pharmaco- logical, physicochemical and chemical properties. Quality control of such medicinal substances requires the deter- mination of indicators characterizing phenolic function. This makes it necessary to study the reactivity and meth- ods of chemical analysis of drugs from the class of phe- nols. The guarantee of the effectiveness and safety of medi- cines is the creation of national standards for their quali- ty. In order to establish the conformity of the quality of medicines to the regulated requirements, it is necessary to use various analytical methods. The conclusion about the quality of drugs depends to a large extent on the quality of the method itself. Therefore, it is necessary to evaluate the suitability of analytical methods for their intended use. However, the State Pharmacopoeia [1] does not always offer the most reliable method for determining the active ingredient in the dosage form. One of the promising methods of quantifying biologi- cally active compounds is the galvanostatic coulometry method [2], characterized by simplicity of the experiment, expressiveness, high accuracy, lack of expensive equip- ment and use in a conventional control and analytical la- boratory. The purpose of this work is to study the possibil- ity of using reactions of electrogenerated titrants with phenolic compounds and to develop a reliable method for their coulometric determination in drugs. http://chimicatechnoacta.ru/ https://doi.org/10.15826/chimtech.2021.8.1.10 http://creativecommons.org/licenses/by/4.0/ Chimica Techno Acta 2021, vol. 8(1), № 20218110 LETTER 2 of 3 2. Results and Discussion The objects of the study were: rutin - as a representative of the class of flavonoids and polyphenols; salicylic acid as a representative of phenolic acids and drugs containing phenolic compounds such as «Ascorutin», «Salicylic Paste» and «Salicylic Ointmen». The titrants used were electrogenated halogens (Cl2, Br2 and I2) and hexacy- anoferrate(III)-ions. Generation was carried out at a con- stant current strength of I = 10 mA, and the equivalence point was fixed biamperometrically with two polarized electrodes on the coulometric analyzer «Expert-006». The selected halogens are not only capable of oxidizing phenol- ic compounds, but also enter into electrophilic substitution reactions of the benzene ring, while the hexacyanofer- rate(III)-ions [Fe(CN)6] 3- are mild oxidizing agents. Based on the studies, we found that the electrogenated hexacyanoferrate(III)-ion and electrogenated iodine enter into redox reactions, but since the redox potential (0.356 V) is low, therefore their oxidative force is not enough to oxidize salicylic acid. Salicylic acid is easily oxi- dized by chlorine, but this reaction proceeds non- stoichiometrically. Therefore, to quantify phenolic acids, an electrogenerated bromine is chosen as the optimal rea- gent from all of us studied, which allows the reactions to be carried out quickly and stoichiometrically. Analysis of salicylic acid content in real objects - drugs «Salicylic paste» and «Salicylic ointment» - confirmed the correct- ness of the choice of electrogenerated bromine as a titrant. There is no information on the mechanism of interac- tion of routine with halogens in the literature. We assume that together with the oxidation of hydroxyl groups, an electrophilic substitution reaction in the benzene ring is also possible. We found that rutin does not interact with the electrogenerated [Fe(CN)6] 3- , while with Cl2 the reac- tion proceeds nonstoichiometrically; and with electrogen- ated bromine and iodine, the reactions are carried out at a molar ratio of rutin:titrant of 1:1 and 1:2, respectively. Therefore, to quantify the routine in real objects, it is rec- ommended to use electrogenerated Br2 and I2 as titrants. In medicinal phenol-containing drugs, ascorbic acid is often contained, as for example, in the «Ascorutin» prepa- ration produced by OJSC «Kiev Vitamin Plant». Ascorbic acid is a potent antioxidant capable of stopping the growth of cancer stem cells. One «Ascorutin» tablet contains ascorbic acid - 0.05 g, routine - 0.05 g and auxiliary sub- stances (sugar, potato starch, calcium stearate, talc). Therefore, we also studied the interaction of ascorbic acid with electrogenerated titrants and found that it with all titants is easily oxidized to dehydroascorbic acid at a mo- lar ratio of ascorbic acid to titrant of 1:1. Results of coulometric determination of ascorbic by re- action with electrogenerated titrant are given in Table 1. The correctness of the determination was checked by the «entered – found» method, the number of tests conducted n = 4, statistical reliability P = 0.95. As can be seen from Table 1, it is better to use halogen titants to quantify ascorbic acid, they are more reactive than [Fe(CN)6] 3- and their use provides very good accura- cy. The determination error, for all titrants as a whole, does not exceed 1.8%, and for halogen titrants within 1%. In living organisms and in dosage forms, the antioxi- dant properties of phenolic compounds always work in tandem with ascorbic acid, so there is a need to develop a method for determining them in the joint presence. We propose a method of joint determination of rutin and ascorbic acid in the preparation «Ascorutin». I2 and Br2 were used as electrogenerated titrants for «Ascorutin». Since the main active substances (rutin and ascorbic acid) in the «Ascorutin» tablets differ in solubility, the following procedure can be proposed for quantitative de- termination. One «Ascorutin» tablet was first treated with ethyl alcohol (96% by weight) and the resulting alcohol extract was titrated with electrogenated bromine and io- dine. The titration results are used to calculate the rutin content of the preparation. The results are shown in Ta- ble 2. Another tablet «Ascorutin» is treated with warm dis- tilled water and the obtained water extract is titrated with electrogenated bromine and iodine. The content of ascor- bic acid in the preparation is calculated from the titration results. The results are shown in Table 3. As shown by the experimental data (Tables 2 and 3), the developed coulometric titration technique with elec- trogenated bromine and iodine is characterized by good reproducibility of results, expressiveness, accuracy and can be used to determine the routine and ascorbic acid in drugs. Table 1 Results of coulometric determination ascorbic acid reaction with electrogenerated titrants (n = 4, Р = 0.95) Power generation titrant entered аscorbic acid, μg found ascor- bic acid, μg Sr, % Br2 180 182 ± 4 0.99 I2 179 ± 3 0.89 Cl2 185 ± 4 1.07 [Fe(CN)6] 3– 191 ± 5 1.8 Hereinafter, Sr is the relative standard deviation. Table 2 Results of coulometric determination of the routine in «Ascorutin» (n = 4, Р = 0.95) Power generation titrant entered tablets «Ascorutin», μg found «Ascorutin» tablets, μg Sr,% Br2 300 294 ± 2 0.99 I2 289 ± 4 0.89 Table 3 Results of coulometric determination of ascorbic acid in «Askorutin» (n = 4, Р = 0.95) Power generation titrant entered tablets «Ascorutin», μg found «Ascorutin» tablets, μg Sr,% Br2 300 295 ± 3 1.08 I2 294 ± 2 1.16 Chimica Techno Acta 2021, vol. 8(1), № 20218110 LETTER 3 of 3 3. Conclusions Thus, the coulometric method we have developed using electrogenerated titrants (Cl2, Br2 and I2 and hexacy- anoferrate(III)-ions) can be recommended for the deter- mination of salicylic acid, ascorbic acid and rutin in their joint presence in dosage forms. The method is character- ized by high reliability, accuracy and expression compared to the Pharmacopoeia method [1], and also eliminates the error of the experiment. References 1. Mashkovsky MD, Babayan EA, Oboimakova AN, Bylaev VM, Severtsev VA, lybimov BI, Sokolov SD, Tentsova AI. Gosudarstvennaya Farmakopeya. Obshchie metody analiza. Lekarstvennoe rastitel’noe syr’yo. [State Pharmacopoeia. General methods of analysis. Medicinal plant raw materials]. Moscow: Medicina; 1990. V. 2. 453 p. Russian. 2. Gruzik TV. Electrochemical determination of the total content of organic acids in wines, wine materials and juices [disser- tation]. Krasnodar (Russia): Kuban State University of Tech- nology; 2015. 123 р.